In the field of drilling, in particular deep borehole engineering, pump devices, in particular immersion pumps, are used to deliver for example hydrocarbons in liquid form and/or thermal water. According to the prior art these pumps are configured as a unit comprising a pump and a motor. This unit operates hundreds of meters down in borehole piping and is thereby in direct contact with the delivery medium, which being a thermal water containing hydrocarbons for example has a high temperature. Because of the hot delivery medium, in particular in the case of thermal water delivery, and due to the waste heat generated during operation of the motor, the pump operating temperature and/or motor operating temperature is/are very high. This has a negative influence on the useful life of the pump and/or motor. In particular the motor, which drives the pump, and generates waste heat due to friction and field losses, is at particular risk when the delivery medium has a high temperature. Also a power supply for the motor has to be conducted downward through the borehole piping by means of a cable that is protected against mechanical damage and water to the actual pump site.
According to the prior art such pump devices are designed so that the pump motor temperature cannot exceed a critical temperature value. The difference between nominal operating temperature and actual operating temperature is a measure of the useful life of pump devices, in particular for the pump motor. If for example the actual operating temperature or even the ambient temperature is already above the nominal operating temperature and also close to the critical temperature value, the useful life of the pump device will be considerably shorter than with operation at nominal operating temperature. Designing for long-term operation at nominal operating temperature can be made difficult or even totally impossible for example due to the following constraints:
The delivery medium, in particular hydrocarbons and/or thermal water, already has such a high temperature itself that operation at nominal operating temperature and the required difference in relation to the critical operating temperature are not ensured.
The required delivery output of the pump is so high that the resulting heat wasted by the motor comes into the region of the critical temperature.
So-called rod pumps are also used in addition to the pump device described above. Such rod pumps have the advantage that the pump can work deep down in the bore piping, while the associated motor is installed above ground. The motor can thus be operated above ground in a relatively non-critical manner in respect of excessive operating temperatures. As the motor and pump are connected mechanically to one another by means of a rod, this solution reaches its delivery limit and/or its mechanical loading capacity at a depth of around 300 m. Such a pump device is already known from U.S. Pat. No. 1,291,407.
It is a particular disadvantage of the prior art that if the motor fails, the complete immersion pump has to be withdrawn from the deep borehole to replace the motor. Such an instance of damage to the immersion pump can result in downtimes of 3 to 4 days.